Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
  • C08J9/28—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof by elimination of a liquid phase from a macromolecular composition or article, e.g. drying of coagulum
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
  • C08J9/28—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof by elimination of a liquid phase from a macromolecular composition or article, e.g. drying of coagulum
  • C08J9/283—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof by elimination of a liquid phase from a macromolecular composition or article, e.g. drying of coagulum a discontinuous liquid phase emulsified in a continuous macromolecular phase
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F2/00—Processes of polymerisation
  • C08F2/32—Polymerisation in water-in-oil emulsions
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J2325/00—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by an aromatic carbocyclic ring; Derivatives of such polymers
  • C08J2325/02—Homopolymers or copolymers of hydrocarbons
  • C08J2325/04—Homopolymers or copolymers of styrene
  • C08J2325/08—Copolymers of styrene

Definitions

• This invention relates to the preparation of low density, porous, crosslinked, polymeric materials.
• the invention relates to reducing curing time in a high internal phase emulsion polymerization process to manufacture low density porous crosslinked polymeric materials.
• Polymeric foams can be generally classified as either closed-cell foams or as open-cell foams.
• Open-cell foams can be used as a matrix to contain various liquids and gases. They are capable of various industrial applications such as, for example, use in wipes and diapers, as carriers and ion exchange resins.
• porous crosslinked polymer blocks which have a very low density and a high capacity of absorbing and retaining liquids.
• Such high absorption capacity, low density, porous polymer blocks can be prepared by polymerizing a specific type of water-in-oil emulsion known as high internal phase emulsion (HIPE) having relatively small amounts of a continuous oil phase and relatively greater amounts of an internal water phase.
• HIPE high internal phase emulsion
• Such high absorption capacity, low density foams are prepared in U.S. Pat. No. 4,522,953 by polymerizing the monomers in the oil phase of a high internal phase water-in-oil emulsion with a water-soluble polymerization initiator such as potassium persulfate. It has been found that in order to obtain foams by this method with high absorption properties and low unreacted monomer content, curing must be conducted for 16 hours or longer at a temperature of 60° C. However, it is desirable to reduce the curing time for a large scale process or a continuous process. Therefore, it will be advantageous to reduce the curing time without significantly affecting the resulting foam properties.
• a process for the production of a porous crosslinked polymeric material comprising the steps of:
• step (c) adding one or more multifunctional unsaturated crosslinking monomers (i) to the one or more vinyl monomers prior to advancing in step (b), (ii) to the advanced monomer component prior to emulsion forming step (e), or to both (i) and (ii) to form an advanced monomer mixture;
• a process in which a branched peroxide is used as the polymerization or an advancement initiator is provided to produce a porous crosslinked polymeric material.
• the time necessary for curing the emulsion is reduced without significantly affecting the resulting foam properties by advancing the monomers prior to forming a water-in-oil high internal phase emulsion.
• foam a low density porous crosslinked polymeric material with high absorption capacity and low monomer content
• foam a low density porous crosslinked polymeric material with high absorption capacity and low monomer content
• foams generally have a dry density of less than about 0.1 g/cc.
• desirable open-cell isoprene or butadiene incorporated foams can be produced by the process of the invention.
• a foam is produced by advancing at least a portion of a monomer mixture containing at least one vinyl monomer and a multifunctional unsaturated crosslinking monomer in the presence of an advancement initiator or by a free-radical-producing radiation source, thereby producing an advanced monomer mixture, then forming a water-in-oil high internal phase emulsion containing such advanced monomer mixture, water as the internal phase and a surfactant and curing the advanced monomers and monomers in such water-in-oil high internal phase emulsion.
• one or more vinyl monomers are advanced in the presence of an effective amount of an advancement initiator or by a free-radical-producing radiation source to produce an advanced monomer component and the multifunctional unsaturated crosslinking monomer is added to the vinyl monomer prior to advancing, to the advanced monomer component prior to emulsion forming, or to both the vinyl monomer and advanced monomer component to form an advanced monomer mixture. Then, a curable high internal phase water-in-oil emulsion is formed containing the advanced monomer mixture, optionally additional vinyl monomers, surfactant, and aqueous solution as the internal phase. Then the advanced monomers and any monomers in the curable emulsion is cured.
• one or more vinyl monomers are advanced in the presence of an effective amount of an advancement initiator or by a free-radical-producing radiation source to produce an advanced monomer component.
• the advanced monomer component is then added and mixed to a water-in-oil high internal phase emulsion containing, in the continuous phase of the emulsion, a monomer component containing one or more vinyl monomers, one or more multifunctional unsaturated crosslinking monomers, or a combination of these monomers to form an advanced monomer emulsion.
• the water-in-oil high internal phase emulsion can be formed in a conventional manner such as those prepared in U.S. Pat. Nos. 4,522,953, 5,149,720 and 5,189,070.
• additional vinyl monomers and additional multifunctional unsaturated crosslinking monomers can be added to the advanced monomer component, to the emulsion, to the advanced monomer emulsion, or to any combination of these.
• Multifunctional unsaturated crosslinking monomers can be added to one or more vinyl monomers to be advanced and advanced along with the vinyl monomers to form the advanced monomer component. If only vinyl monomers are present in the emulsion, one or more multifunctional unsaturated crosslinking monomers can be added to one or more monomers to be advanced, advanced monomer component, to the emulsion, to the advanced monomer emulsion, or to any combination of these in an effective amount to crosslink the monomers to form a foam. Then the advanced monomers and any monomers in the advanced monomer emulsion are cured.
• the term "advancement” or “advanced” includes any oligomerization or partial polymerization of some of all of the monomers.
• the advanced monomers thus generally contain a mixture of monomers, and various oligomers/polymers.
• the advancement may be carried out, for example, by mixing the entire monomer mixture together with an advancement initiator, warming to an effective temperature for polymerization and oligomerizing the mixture, or a single component or selected components may be advanced in a similar fashion by themselves and then blended with the rest of the monomers desired in the continuous phase of the emulsion or blended into a water-in-oil high internal phase emulsion containing the rest of the monomers.
• an advancement initiator warming to an effective temperature for polymerization and oligomerizing the mixture
• a single component or selected components may be advanced in a similar fashion by themselves and then blended with the rest of the monomers desired in the continuous phase of the emulsion or blended into a water-in-oil high internal phase emulsion containing the rest of the monomers.
• part or all of the monomers may be advanced, and the advanced product may be blended with other monomers for subsequent advancement steps if desired before using the advanced monomers to form a high internal phase water-in-oil emulsion, blended with additional components and forming the emulsion later, or blended into a conventional high internal phase water-in-oil emulsion.
• Suitable vinyl monomers include, for example, monoalkenyl arene monomers such as styrene, ⁇ -methylstyrene, chloromethylstyrene, vinylethylbenzene and vinyl toluene; acrylate or methacrylate esters such as 2-ethylhexyl acrylate, n-butyl acrylate, isobutyl acrylate, t-butyl acrylate, hexyl acrylate, n-butyl methacrylate, lauryl methacrylate, and isodecyl methacrylate; conjugated diolefins such as butadiene, isoprene and piperylene; allenes such as allene, methyl allene and chloro
• Suitable crosslinking agents can be any multifunctional unsaturated monomers capable of reacting with the vinyl monomers.
• Multifunctional unsaturated crosslinking monomers include, for example, difunctional unsaturated crosslinking monomers such as divinyl benzene, diethylene glycol dimethacrylate, 1,3-butanediol dimethacrylate, and allyl methacrylate; tri-, tetra- and penta-functional unsaturated crosslinking monomers such as trimethylolpropane trimethacrylate, pentaerythritol tetramethacrylate, trimethylolpropane triacrylate, pentaerythritol tetraacrylate, glucose pentaacrylate, glucose diethylmercaptal pentaacrylate, and sorbitan triacrylate; and poly-functional unsaturated crosslinking monomers such as polyacrylates (eg.
• Crosslinking monomers are typically present in an amount of from about 2 weight percent to about 70 weight percent, preferably from about 5 weight percent to about 40 weight percent based on the total monomer mixture. Some of these crosslinking monomers can be incorporated as a non-crosslinked monomer as long as at least about 2 weight percent of the crosslinking monomers are crosslinked.
• Suitable advancement initiators are monomer-soluble free radical polymerization initiators.
• Monomer-soluble (oil soluble) free radical polymerization initiators include, for example, azo compounds such as azobisisobutyronitrile (AIBN) and peroxides such as benzoyl peroxide, methyl ethyl ketone peroxides, di-2-ethylhexyl peroxydicarbonate and other alkylperoxycarbonates and alkylperoxycarboxylates including branched peroxides listed below.
• the advancement initiator should be present in at least an amount effective to partially polymerize or oligomerise the monomers, but can also be in an amount effective to completely polymerize and crosslink the monomers.
• the advancement initiator can be present from about 0.005 to about 20 weight percent, preferably from about 0.1 to about 4 weight percent based on the monomers.
• the advancement initiator is added to the monomer mixture containing one or more vinyl monomers with or without the crosslinking monomer and optionally a surfactant.
• Suitable free-radical-producing radiation sources are gamma rays, electron beams, neutrons, ultra-violet or other agents capable of inducing free-radical formation.
• the monomers will generally be exposed to the radical forming source until suitable viscosity is reached.
• free-radical-producing radiation sources are employed to perform the advancement or cure step, their use during an advancement step offers several advantages: smaller amounts of material, allowing thinner flows or vessels to be treated, commensurate with the penetrating power of these radiations; lack of wastage of energy on the inert internal phase, resulting in higher efficiency; and avoidance of the risk of destabilization of the emulsion by the impingement of the radiation (e.g., in the case of electron beams or other particle beams).
• the monomer mixture is advanced (partially-polymerized) to provide a ratio of viscosity of monomer mixture to water within the range of from about 1000:1 to above 1:2, more preferably from about 50:1 to about 1.5:2. Generally, the ratio of viscosity for a non-advanced monomer to water is about 1:2.
• the viscosity of the advanced monomer mixture will vary depending on the monomer used.
• the viscosity of the advanced monomer will be higher than the viscosity of the unadvanced monomer mixture.
• the viscosity is also dependent on temperature, and is quite low at ambient temperature, typically about 0.4 cp for the unadvanced monomer mixture, and up to about 100 cp for the advanced monomer mixture.
• the viscosity will be expressed as a ratio between the viscosity of the monomer mixture and that of the advanced monomer mixture, or the viscosity of the advanced monomer mixture plus surfactant and the unadvanced mixture plus surfactant, because the absolute viscosity values are a function of temperature and whether or not the surfactant has been added to the mixture (normally addition of the surfactant raises the viscosity several-fold). If the advanced mixture is in the numerator, and the non-advanced (fresh) in the denominator, then the ratio should be greater than 1.00 to show advancement. Preferably, the ratio is within the range from about 1.03 to about 50, more preferably from about 1.07 to about 30, most preferably from about 1.15 to about 15.
• the ratio is too low, little acceleration of cure time results, but cured foam properties are about those of the unadvanced foam. If the ratio is too high, considerable acceleration of cure time results, but the high viscosity and changed solubility parameters of the largely oligomerized/polymerized mixture may make it difficult to form the proper emulsion. Also as the ratio becomes high, it is very hard to quench the advancement reaction to give a precisely reproducible material. This quenching is easiest if the viscosity ratio is less than about 10, preferably less than about 5. If only a part of the monomer mixture is advanced, the ratio applied to the advanced part may be different, normally a higher ratio, depending on how much of the monomer is advanced.
• the viscosities are generally low, it is convenient to measure them at -78° C.
• the viscosity of a 1:1:3 weight percent mixture of styrene: divinyl benzene: 2-ethylhexyl acrylate is about 300 cp at -78° C.
• the viscosity at -78° C. increases to about 2900 cp.
• the level of advancement preferred will depend on the particular mixture of monomers and the relative importance of rapid cure, volatility and properties.
• the monomer mixture is heated in the presence of the advancement initiator at a temperature above about 25° C., preferably at a temperature within the range of about 25° C. to about 150° C., more preferably within the range of about 50° C. to about 100° C. for a time effective to form the advanced monomer mixture with a desired viscosity, or irradiated by a free-radical-producing radiation source for a time effective to form the advanced monomer mixture with a desired viscosity.
• Such time is preferably within the range of about 5% to about 95% of the time necessary to form a solid mixture.
• the mixture is solid when the mixture no longer visibly deforms.
• the time necessary to form a solid mixture can be conveniently measured by a Solidity Test described below.
• a Solidity Test described below.
• the viscosity of the monomer mixture exceeds that of honey at 25 ° C., it is difficult to form a good emulsion depending on the monomer mixture. Also, greater levels of free water may result after cure when highly advanced monomer solutions are used.
• the advancement is done for a time within the range of about 10% to about 90%, most preferably from about 35% to about 88% of the time necessary to form a solid mixture.
• the advanced monomer mixture which is preferred is one which forms a stable emulsion, cures rapidly, and yields a good porous polymeric product relative to the unadvanced monomer mixture.
• Advancement of the monomer mixture has various advantages besides the acceleration of cure time of the emulsion described above; among these is the ability to use comonomers which are not effective when used directly in the conventional emulsion system such as isoprene and butadiene, the reduction of volatiles from the emulsion curing line, the reduction of soluble organics in recycle water, the elimination of odors, and the use of low boiling monomer mixtures at atmospheric pressure.
• the shorter cure time in the emulsion process is advantageous due to the smaller curing ovens or continuous process facilities, which result in an overall simplification due to the low volume of the monomer steam (typically 110th to 150th of the emulsion stream resulting from it).
• the monomer steam typically 110th to 150th of the emulsion stream resulting from it.
• it requires typically only 1 gallon of reactor space to advance the monomer for each 30 gallons of reactor space required to cure the emulsion.
• the level of unsaturation in a mixture of monomers containing double bonds may be assessed by various means, such as infrared determination of the C ⁇ C stretching frequency, NMR examination of the vinylic carbons or protons, ultraviolet absorption measurements, dielectric constant, average molecular weight by HPLC, or other means of measuring molecular weight or unsaturation.
• Level of advancement which is preferred will correlate with the ratioed times previously described. Once the relationship to the ratioed time is determined, such tests serve essentially as a quality control method.
• the monomer can be mixed with comonomers, such as styrene, divinylbenzene, acrylates, and/or the like, in the presence of an advancement initiator in a sealed reaction vessel, and the reaction vessel warmed to a temperature effective to begin an oligomerization and/or polymerization reaction.
• comonomers such as styrene, divinylbenzene, acrylates, and/or the like
• the vessel may be vented and depressured or evacuated, to remove unreacted vinyl chloride monomer, and leave a polymerizable liquid "advanced monomer" mixture containing vinyl chloride molecules incorporated into larger molecular structures.
• This advanced monomer then can be polymerized with less potential health hazard of handling vinyl chloride in the mixture, but with the property benefits of the final vinyl chloride containing polymer structure.
• low boiling monomers such as butadiene or isoprene can be readily incorporated in the HIPE foam material either by a monomer mix approach in which a mixture of one or more low boiling monomers, optionally other vinyl monomers, and a crosslinker is advanced preferably until up to about 1/3 of the monomer is used, or the low boiling component itself can be advanced and then blended with the higher boiling components.
• a monomer mix approach in which a mixture of one or more low boiling monomers, optionally other vinyl monomers, and a crosslinker is advanced preferably until up to about 1/3 of the monomer is used, or the low boiling component itself can be advanced and then blended with the higher boiling components.
• 1,3-butadiene it can be done by advancing the butadiene itself to a desired level of molecular weight and low volatility, or suitable level of reaction instead of advancing the entire monomer mixture.
• an autoclave or a pressure reactor can be charged with liquid butadiene, and purged of air by venting some of the butadiene, or alternatively, by chilling the butadiene in liquid nitrogen or in dry ice, and evacuating the gas cap of permanent gases.
• a suitable advancement initiator such as t-butyl peroxyisobutyrate to advance the butadiene is charged to the reaction vessel.
• the reaction vessel is then warmed to about 80° C. -85° C.
• the advancement reaction for low boiling monomers is preferably carried out until the absolute pressure in the reaction vessel at room temperature is less than about 14.7 psia (or below boiling) at atmospheric pressure.
• the absolute pressure in the reaction vessel should be reduced to a pressure at most of about 60 psia at 82° C. to indicate a level of reaction just sufficient to prevent boiling at 27° C. (80° F.).
• the pressure at the reaction temperature will vary depending on the monomer mixture advanced.
• the absolute pressure may be higher than about 60 psia at 82° C. if a mixture of monomers such as advanced butadiene and styrene monomers are mixed before emulsification due to the lower partial pressure of styrene as long as the absolute pressure in the reaction vessel at the handling temperature is less than about 14.7 psia.
• the reaction may be continued to a lower pressure, for example to about 20 psig at 82° C. which will give about 8.5 psia at 27° C. (80° F.).
• High levels of advancement may cause the diene monomers to crosslink sufficiently via 1,2-polymerization to gel.
• a different initiator may be used or a solvent (eg., inert diluent such as hydrocarbons including cyclohexane, carbon tetrachloride and benzene) or other modifier (eg., functional modifier such as tetrahydrofuran and quinuclidine) may be used to affect the course of the reaction by dilution or by reaction modification.
• the monomer mixture may be advanced to a lesser degree, and the excess monomer vented to recycle to lower the pressure of the remaining portions which will be utilized in the process.
• the advanced monomer mixture can be optionally blended with other monomer components to further lower the vapor pressure of the monomer mixture and make the emulsification and curing process simpler.
• a wide range of temperature may be used to perform the advancement depending on the initiator and the monomer used. For example, for 1,3-butadiene, higher or lower temperatures than about 80° C.-85° C. may be used, but the temperature should be below about 152° C., the critical temperature of butadiene, so that the monomer may remain in the liquid instead of the supercritical gas state. In addition, the temperature should be below the ceiling temperature of the oligomers formed to allow polymerization to occur.
• the temperature should be high enough to give a satisfactory rate with whatever initiator system is used.
• the temperature preferred for the advancement reaction will be within the range from about room temperature to about 150° C., more preferably from about 50° C. to about 100° C.
• the advanced component is to be a major component (more than 50% by weight of the foam), a lower number average molecular weight of preferably less than about 1000, and most preferably less than about 500, of the advanced component is desired.
• allene, of molecular weight 40 and boiling point of -35° C. may be selectively dimerized using a suitable initiator to give a mixture of cyclohexadienes, hexatriene, dimethylene cyclobutanes, vinyl methylene cyclopropanes, and bicyclic structures having a molecular weight of 80 and boiling range of about 65° C. to about 82° C. In this event, the vapor pressure of the advanced monomer system is greatly reduced while the number average molecular weight is doubled.
• a similar change in vapor pressure will require the formation of higher molecular weight species due to molecular heterogeneity of the advanced sample.
• the advanced mixture will contain a mixture of macromolecules with different degrees of polymerization/oligomerization, including unreacted monomers.
• Such oligomerization/polymerizations typically have a ratio, Q, of weight average to number average molecular weight, of 2.
• Q ratio
• the advanced volatile monomer mixture can be combined with crosslinking monomers and/or reactive low volatility diluents (e.g. styrene, and methyl methacrylate) to produce a polymerizable oil phase which may then be further advanced (if desired to improve properties or handling) or emulsified and cured directly.
• the volatile monomers can be combined with the crosslinking monomers and/or reactive low volatility diluents before advancement and advanced together.
• the monomer mixture Before emulsification, the monomer mixture will be combined normally with suitable oil soluble surfactants, although suitable surfactants could alternatively be dispersed in the aqueous phase before emulsification.
• suitable surfactants could alternatively be dispersed in the aqueous phase before emulsification.
• the surfactant can be added at any stage to the monomer mixtures, before or after advancement.
• the monomer mixture may have additional initiator added to promote the cure of the emulsion, it may cure using the initiator added for the advancement step or one or more additional and different initiators may be added.
• additional initiator added to promote the cure of the emulsion
• it may cure using the initiator added for the advancement step or one or more additional and different initiators may be added.
• Many variations, modifications, and extensions of these illustrative cases can be used as long as at least a portion of the monomer mixture, whether one monomer component or part of a mixture of monomers, is advanced prior to emulsification.
• branched alkyl carbonate peroxides branched at the 1-carbon position or branched alkyl carboxylate peroxides branched at the ⁇ -carbon position and/or 1-carbon position cure faster than the conventional oil-soluble initiator such as benzoyl peroxide.
• This branching at the 1-carbon position and/or ⁇ -carbon position can be secondary or tertiary.
• the high internal phase water-in-oil foams can be cured by the branched peroxides to completion without the addition of additional polymerization initiator, although for faster cure time additional polymerization initiator can be added.
• the preferred branched alkyl carbonate peroxide can be represented by the formula: ##STR1## where R 1 is independently C 1 to C 16 hydrocarbon groups or hydrogen in which at least two of the R 1 are hydrocarbon groups. Hydrocarbon groups can be alkyl, alkenyl or aryl groups.
• the preferred branched alkyl carboxylate peroxide can be represented by the formula: ##STR2## where R 1 and R 2 are independently C 1 to C 16 hydrocarbon groups or hydrogen in which at least two of the R 1 or R 2 are hydrocarbon groups. Preferably at least two of both R 1 and R 2 are hydrocarbon groups. Hydrocarbon groups can be alkyl, alkenyl or aryl groups.
• branched peroxides examples include t-butyl peroxyisobutyrate, t-butyl peroxycrotonate, t-butyl peroxypivalate, di-isobutyryl peroxide, di-t-butyl diperoxyphthalate, t-butyl perbenzoate, cumylperoxy neodecanoate, 2,5-dimethyl-2,5-bis(benzoylperoxy)hexane, 2,5-dimethyl-2,5-bis(2-ethylhexanoylperoxy)hexane, t-butyl peroctoate, 1,1,3,3-tetramethylbutylperoxy-2-ethyl hexanoate, dicyclohexyl peroxydicarbonate, di(sec-butyl) peroxydicarbonate, diisopropyl peroxydicarbonate, and t-butyl peroxyisopropylcarbonate.
• branched peroxide examples include LupersolTM 11, LupersolTM 80, LupersolTM 118M75, LupersolTM 225, LupersolTM 227, LupersolTM 229, LupersolTM 256, LupersolTM 259, LupersolTM KBD, LupersolTM TBIC, LuperoxTM 118, LuperoxTM 229, and LuperoxTM IPP (from Atochem North America).
• the most preferred advancement and/or polymerization initiator is t-butyl peroxyisobutyrate.
• branched peroxide initiators also improve the conventional water-in-oil high internal phase polymerization processes such as those described in U.S. Pat. No. 4,522,953 where no advancement takes place prior to the formation of an emulsion. Further these branched peroxide initiators are also useful when the initiator is added after the formation of the emulsion as described in U.S. Pat. No. 5,210,104, issued May 11, 1993.
• polymerization initiators such as benzoyl peroxide, AIBN and methyl ethyl ketone peroxide
• additional polymerization initiator should be added in the aqueous mixture or in the emulsion.
• the polymerization initiators can be, for example, oil-soluble (monomer-soluble) initiators such as branched peroxides listed above or water-soluble initiators such potassium or sodium persulfate and various redox systems such as ammonium persulfate together with sodium metabisulfite.
• the polymerization initiators can be any of the water-soluble initiators mentioned above.
• the additional polymerization initiator When the additional polymerization initiator is added to the emulsion, it can optionally be blended into the emulsion by any blending technique such as, for example, a static mixer or a pin mixer at a low shear rate, to form a curable water-in-oil high internal phase emulsion.
• the rate of shear must be high enough to blend the initiator but low enough not to allow the emulsion to coalesce or liquify.
• Such shear rate should be such that the initiator-added emulsion (i.e, curable water-in-oil high internal phase emulsion) is at least blended sufficiently to form a substantially uniform emulsion but less than the inherent shear stability point.
• the inherent shear stability point is shear at which the emulsion coalesces due to excess shearing.
• the surfactant used in making the high internal phase emulsion which is to be polymerized is also important in forming the water-in-oil high internal phase emulsion.
• the surfactant can be added to the aqueous phase or monomer phase (monomer mixture) depending on the solubility of the surfactant used.
• Suitable surfactants include, for example, nonionic surfactants such as sorbitan esters (eg., sorbitan monooleate and sorbitan monolaurate), glycerol esters (eg.
• glycerol monooleate and glycerol monoricinoleate PEG 200 dioleate, partial fatty acid esters of polyglycerol, and castor oil 5-10 EO; cationic surfactants such as ammonium salts (eg., distearyl dimethyl ammonium chloride and dioleyl dimethyl ammonium chloride); and anionic surfactants such as bis-tridecyl sulfosuccinic acid salt.
• Commercially available surfactants include, for example, SPAN® emulsifying agents 20, 40, 60, 65, 80 and 85 (from Fluka Chemical Corp.
• EMSORB 2502 from Henkel
• ALKAMULS® sorbitan esters SML, SMO, SMS, STO and ALKAMULS® sorbitan ester ethoxylates PMSL-20 and PSMO-20 from Alkaril Chemicals Ltd.
• a combination of sorbitan esters can also be used as described in U.S. Pat. No. 5,200,433 issued Apr. 6, 1993.
• the amount of surfactant must be such that a water-in-oil high internal phase emulsion will form.
• the surfactant is present in an amount effective to form a water-in-oil high internal phase emulsion (HIPE).
• the surfactant can be present from about 2 to about 40% by weight, more preferably about 5 to about 25% by weight based on the monomers.
• the relative amounts of the aqueous phase containing water and an electrolyte and monomer phase containing monomer mixtures and/or advanced monomer mixtures used to form the high internal phase emulsions are a factor in determining the structural, mechanical and performance properties of the resulting polymeric foams.
• the ratio of water to oil in the emulsion can influence the density, cell size, and specific surface area of the foam products.
• the water-in-oil high internal phase emulsion typically contains as the internal phase, at least about 90 weight percent, based on the emulsion, of water, corresponding to a water to oil weight ratio of at least about 9:1, more preferably at least about 95 weight percent of water, most preferably at least about 97 weight percent of water, corresponding to a water to oil weight ratio of at least about 33:1.
• the internal aqueous phase can preferably contain a water-soluble electrolyte to stabilize the HIPE and to make the foam more water wettable.
• Suitable electrolytes include inorganic salts (monovalent, divalent, trivalent or mixtures thereof), for example, alkali metal salts, alkaline earth metal salts and heavy metal salts such as halides, sulfates, carbonates, phosphates and mixtures thereof.
• Such electrolyte includes, for example, sodium chloride, sodium sulfate, potassium chloride, potassium sulfate, lithium chloride, magnesium chloride, calcium chloride, magnesium sulfate, aluminum chloride and mixtures thereof.
• Mono- or di-valent salts with monovalent anions such as halides are preferred.
• a water-in-oil high internal phase emulsion is dependent on a number of factors such as the monomers used, water to oil ratio, type and amount of surfactant used, mixing conditions, and presence and the amount of water-soluble electrolyte. Unless all of these factors are such that they favor formation of a water-in-oil emulsion, the emulsion will be an oil-in-water emulsion rather than water-in-oil high internal phase emulsion.
• the formation of a water-in-oil emulsion is described in U.S. Pat. No. 4,522,953, the disclosure of which is herein incorporated by reference.
• the water can be mixed in any way up to a water to oil ratio of about 4:1
• An oil-in-water emulsion becomes preferred if the water is added all at once beyond a water to oil ratio of about 4:1.
• the water must be added gradually with a moderate rate of shear.
• a small capacity mixer such as a paint mixer with a shear rate of at least about 5 s -1 , preferably at east about 10 s -1 , can be used to mix the water-in-oil emulsion.
• a larger mixer equipped with an impeller with a shear rate of at least about 10 s -1 or a pin gap mixer with a shear rate of at least about 50 s -1 , preferably at least about 100 s -1 , can also be used. If the shear rate is too low, the water-in-oil emulsion will revert to an oil-in-water emulsion. It is desirable to at least have a water to oil ratio of about 9:1, preferably at least about 19:1, more preferably at least about 30:1 for a high absorbency capacity foam.
• An HIPE can be prepared in batches or continuously.
• the emulsion is formed in a vessel or a container by gradually adding an aqueous phase to an advanced monomer mixture under a moderate rate of shear until the desired water to oil ratio is reached.
• An HIPE can be prepared continuously by initially preparing a preformed emulsion of approximately the same character as the desired emulsion by the method described above, then introducing into the preformed emulsion, both the aqueous phase and advanced monomer phase of the emulsion in such proportions so as to produce the desired emulsion while maintaining the emulsified mass in a state of continuous shear which reduces the effective viscosity but not above the inherent shear stability point of the desired emulsion, and then withdrawing the prepared emulsion at the desired rate.
• the aqueous phase and the advanced monomer phase for batch and continuous processes can be introduced into a mixing vessel by an aqueous stream or a monomer stream, respectively, through one or more inlets.
• the streams can be combined prior to or after entering the mixing vessel, then mixed in such a way to produce the desired HIPE.
• the mixing vessel is any container in which the high internal phase emulsion is made regardless of the type of mixer or mixer head used.
• the curable water-in-oil high internal phase emulsions can be cured in a batch process or in a continuous process.
• the curable HIPE is collected in a suitable container with the desired shape and cured at a temperature of at least about 25° C. for a time effective to polymerize and to cure the monomers.
• the HIPE is preferably polymerized and crosslinked (cured) at a temperature within the range of about 25° C. to about 90° C., as long as the emulsion is stable at the curing temperature.
• a multiple-step process as described in a U.S. Pat. No. 5,189,070 issued Feb. 23, 1993 can also be used, the disclosure of which is herein incorporated by reference.
• the emulsion is precured at a temperature of less than about 65° C. until the emulsion has a Rheometrics dynamic shear modulus of greater than about 500 pascal, (lightly gelled, having a consistency like a jelly or a gelatin referred to as "gel"), then cured at a temperature of above about 70° C. for a time effective to cure the gel.
• the cure temperature can be as high as about 175° C. under suitable pressure to prevent water from boiling.
• the emulsions can be heated, for example, by hot water, hot air, steam, IR, RF, microwave or ohmic heating.
• the HIPE should be cured until the desired properties are obtained.
• the emulsions should be cured for at least about 4 hours at 60° C. or at least about 1/2 hour at 60° C. then 3 hours at a temperature of above about 70° C.
• the extent of reaction after curing is at least about 85% of the monomers, preferably at least about 90%, more preferably at least about 95% (i.e., less than about 5% of free monomers), most preferably at least about 99% (i.e., less than about 1% of free monomers) in order to obtain good properties.
• foams can be post-cured to improve the foam properties. Better properties such as, for example, increased free swell (i.e., amount of liquid a foam can initially absorb), and/or good resistance to compression deflection (i.e., retention of liquid under load) can be obtained depending on the monomer formulation by post-curing the foam at a temperature of above about 75° C., preferably greater than 90° C., by steam, hot air or other heating source. Such heating may be performed initially in a heat exchanger, oven, over heated rollers or by other means.
• pressure is preferably applied to keep the water in the liquid phase and to obtain better properties. If desired, the pressure may be lowered to boil some of the water, but in normal practice the water will be maintained in the liquid state to stabilize the monomer.
• the use of pressure to maintain the aqueous phase and oil phase in the liquid state allows very rapid curing of emulsions at very high temperatures, provided the emulsions are stable at the high temperatures used.
• Pressure can be applied to the emulsion, if desired, at a pressure generally from above atmospheric pressure, typically within the range of about atmospheric pressure to about 1.03 MPa (150 psig).
• a pressure from about 7 to 70 kPa gauge (about 1 to 10 psig) is sufficient; when the temperature is about 130° C., a pressure from about 210 to 480 kPa gauge (about 30 psig to 70 psig) is preferred.
• the emulsion can be cured under pressure by using an autoclave operating under autogenous pressure of steam generated from pure water at a given temperature, by applying nitrogen or air pressure to prevent boiling of the emulsion or by mechanical means, such as rollers, pistons, molds, or the like.
• the water incorporated in the foam may be squeezed out, dried by heat or flashed by lowering the pressure to a suitable level to evaporate the remaining liquid to give the desired degree of dryness in the product foam.
• drying techniques will preferably be used after the desired state of cure is developed in the foam material.
• foams prepared by the inventive process may be washed prior to, after or between drying stages to yield an absorbent block which is especially useful for the absorption of liquids.
• these foams are washed to reduce the electrolyte content of the foam with a solvent such as, for example, an alcohol, a low concentration electrolyte solution (lower concentration than the water phase) such as 1% calcium chloride solution or deionized water.
• a solvent such as, for example, an alcohol, a low concentration electrolyte solution (lower concentration than the water phase) such as 1% calcium chloride solution or deionized water.
• the washed foams can be conveniently dried by squeezing the water and/or solvent out of the foams and air or heat drying.
• the foams produced by the inventive process possess high absorption capacities and good uniform properties especially suitable for use as liquid absorbent articles.
• a flat-tipped probe of about 6 mm diameter is placed on top of an advanced monomer mixture to create a pressure at the flat-tip of about 2.1 kPa (0.3 psi). The ease and penetration of the object into the gel was measured. The monomer mixture is considered solid when the object no longer penetrates or penetrates less than about 1 mm.
• aliquots of approx. 5 ml are removed and placed in 8 dram vials. If the aliquots are above ambient temperature, the aliquots are then quickly cooled in wet ice to ambient temperature (approx. 24 ° C.). The aliquots are chilled in acetone/dry ice slush bath for approx. 10 minutes to a temperature of approx. -78° C. The warm aliquots may be chilled immediately to approx. -78° C. While the aliquots are kept cold, the viscosity is run using Brookfield Viscometer, Model RVTD equipped with a #6 Spindle (manufactured by Brookfield Engineering Lab, Stoughton, Mass.).
• bromine number solvent consisting of acetic acid, trichloroethylene, methanol with 1% sulfuric acid and 1/5% water from Ricca Company.
• a suitable solvent is 1400 ml of acetic acid, 268 ml of methylene chloride, 268 ml of methanol, and 36 ml of a 1:5 mixture of sulfuric acid and water.
• 100 Milligrams of sample is dissolved in 100 ml of the solvent and then titrated with 0.5N bromine/bromate titrant in a Kyoto AT310 potentiometric titrator. The titration is done in a sealed cell kept between 0° C. to 5° C., using a platinum double ring electrode.
• the level of saturation of the solution with bromine is followed potentiometrically, and the bromine number values are reported as grams of bromine reacted per 100 grams of sample.
• FS Free Swell
• DT Dry Thickness
• FD Finam Density
• RTCD Percent Strain/Resistance to Compression Deflection
• a 2" ⁇ 2" (5.08 ⁇ 5.08 cm) square is cut from a foam slice.
• the thickness of the foam sample is measured while it is dry (“dry thickness") using a dead weight thickness gage (a digital linear gage model EG-225 made by Ono Sokki) exerting 50 grams force applied to a 1.60" diameter disk. This thickness is called the “caliper.”
• the foam square is soaked in warm 88° F. (31° C.) Syn-Urine from Jayco for 17 minutes. From the 2" ⁇ 2" (5.08 ⁇ 5.08 cm) square, a circle of 1.129" (2.868 cm) diameter is cut. This disk is re-equilibrated in the Syn-Urine for 5 minutes. The wet disk is then weighed ("initial wet weight").
• the thickness of the wet sample is measured using the same load gage ("initial wet caliper").
• the disk is then placed under a 5.1 kPa (0.74 psi) stress where stress is the total dead weight applied to the gage divided by the cross-sectional area.
• the thickness of the disk is measured under this stress after 15 minutes (“wet caliper"). After 15 minutes, the specimen disk is weighed to measure the retained fluid.
• the excess urine is squeezed from the disk and the remainder of the square from which it was cut.
• the foam is placed in boiling deionized water for 15 minutes. The foam is washed this way several times to remove inorganics. The foam is then removed, blotted dry, then placed in a vacuum oven at 60°-70° C. and dried until the foam has fully expanded. The weight of the dry disk sample is then determined in grams ("final dry weight").
• VWT Vertical Wicking Time
• a 1 to 2 cm wide strip is cut, greater than 5 cm in length.
• the strip of foam is clamped or taped to a metal ruler, with the bottom of the foam strip flush with the 0 mark on the ruler.
• the ruler and foam are placed in a container of approximately 100 ml Syn-Urine from Jayco, in an incubator at 99° F. (37° C.) so the bottom of the strip (0 mark) is barely touching the surface of the Syn-Urine (less than 1 mm).
• the Synurine is dyed with food coloring to more easily monitor its absorption and rise in the foam.
• a stopwatch is used to measure the time required for the liquid level to reach 5 cm vertical height in the foam sample.
• the amount of unabsorbed water was measured by decanting fluid from the foam in the container after pre-curing or curing stage and weighing the decanted fluid.
• This example demonstrates the change in viscosity as measured at -78° C. as the monomer mixture is advanced according to the invention.
• a 1:1:3 weight ratio of styrene: divinyl benzene: 2-ethylhexyl acrylate was mixed to produce a monomer mixture and viscosity was measured at -78° C.
• styrene divinyl benzene: 2-ethylhexyl acrylate
• Viscosity was measured at -78° C.
• a sorbitan monolaurate surfactant (SPAN® 20 emulsifying agent from Fluka Chemical Corp. or Aldrich Chemical Co.) was added and viscosity was measured at -78° C.
• a 1:1:3 weight ratio of styrene: divinyl benzene: 2-ethylhexyl acrylate was mixed to produce a monomer mixture.
• styrene divinyl benzene: 2-ethylhexyl acrylate
• a monomer mixture 12 parts by weight for 100 parts by weight of the monomer mixture of a sorbitan monolaurate surfactant (SPAN® 20 emulsifying agent from Fluka Chemical Corp. or Aldrich Chemical Co.) was added and bromine number was measured as described above.
• a sorbitan monolaurate surfactant (SPAN® 20 emulsifying agent from Fluka Chemical Corp. or Aldrich Chemical Co.) was added and bromine number was measured as described above.
• the available double bonds have decreased 14% over the advancement time.
• the particular test used did not give a reliable indication for acrylate double bonds, which reacted more slowly than the styrenic double bonds.
• the bromine numbers are low relative to the theoretical numbers for the monomer mixture.
• the data show a clear drop in number of reactive double bonds with time of advancement which can be used to monitor the degree of advancement.
• This example demonstrates the change in bromine numbers as the monomer mixture containing a volatile monomer is advanced according to the invention.
• the available bromine double bonds have decreased about 21% over the advancement time. Since the isoprene polymers mostly retain a reactive double bond for each isoprene unit, the 21% observed decrease in double bonds represents from 21% to 42% of complete polymerization cure (depending on whether the monomer has both or only one bond reacted).
• LupersolTM 80 initiator gives a greater degree of advancement at a shorter time when held at 80 to 87° C. although the Self Accelerating Decomposition Temperature (SADT) of LupersolTM 80 initiator is higher than for LupersolTM 225, 223 or 188M75 initiators (80° C. versus 0° C., 0° C. and 15° C. respectively).
• SADT Self Accelerating Decomposition Temperature
• the amount of advancement is not just a function of the amount of peroxide decomposed but the matching of the rate of decomposition to the rate of polymerization. (The half life at 80° C.
• the 1-position or ⁇ -position branched peroxides such as di(sec-butyl) peroxydicarbonate, t-butyl peroxyisobutyrate and alpha-cumyl peroxyneodecanoate are clearly more effective at advancing the monomers than peroxides not branched at the 1-position or ⁇ -position such as di(2-ethylhexyl) peroxydicarbonate.
• a 1:1:3 weight ratio of styrene: divinyl benzene: 2-ethylhexyl acrylate were mixed to produce a monomer mixture.
• Synercial divinyl benzene containing 55% divinyl benzene from Aldrich Chemical Co. was used.
• 12 parts by weight for 100 parts by weight of the monomer mixture of a sorbitan monolaurate surfactant was added and bromine number was measured as described above.
• This example demonstrates preparation of a low density crosslinked polymeric material by advancing the monomer mixture according to the invention.
• a monomer mixture (19.11 wt % styrene, 20.63 wt % divinyl benzene and 60.26 wt % of 2-ethyl hexyl acrylate) is mixed with 1.06 g of t-butyl peroxyisobutyrate (LupersolTM 80 from Atochem North America).
• t-butyl peroxyisobutyrate LiupersolTM 80 from Atochem North America.
• divinyl benzene commercial divinyl benzene containing 55% divinyl benzene from Aldrich Chemical Co. was used.
• To 80.03 g of the initiator-containing monomer mixture which has been heated for 12 minutes in a 80° C.
• the remaining emulsion (521.41 g) was poured into a 1.4 liter (3 US pint) tub and labeled B2.
• the emulsion was cured by placing this jar B1 in a 60° C. water bath and periodically tested with a flat-tipped probe of about 6 mm diameter which creates a pressure at the flat-top of about 0.3 psi ("the probe") by placing the probe on top of the emulsion. After 136 minutes, the probe sat on top of the foam and did not sink.
• the emulsion in the tub was cured by heating the tub B2 in a 60° C. incubator for 24 hours. 3.13 % of free water was poured off from the resulting foam.
• the probe After 121 minutes, the probe sat on top of the foam and did not sink.
• the emulsion in the tub was cured by heating the tub C2 in a 60° C. incubator for 24 hours. 2.74 % of free water was poured off from the resulting foam.
• the probe After 112 minutes, the probe sat on top of the foam and did not sink.
• the emulsion in the tub was cured by heating the tub D2 in a 60° C. incubator for 24 hours. 2.08 % of free water was poured off from the resulting foam.
• the probe After 94 minutes, the probe sat on top of the foam and did not sink.
• the emulsion in the tub was cured by heating the tub E2 in a 60° C. incubator for 23 hours. 1.77 % of free water was poured off from the resulting foam.
• the probe After 134 minutes, the probe sat on top of the foam and did not sink.
• the emulsion in the tub was cured by heating the tub G2 in a 60° C. incubator for 22 hours. 4.94 % of free water was poured off from the resulting foam.
• the probe After 132 minutes, the probe sat on top of the foam and did not sink.
• the emulsion in the tub was cured by heating the tub H2 in a 60° C. incubator for 21 hours. 6.8 % of free water was poured off from the resulting foam.
• the probe After 119 minutes, the probe sat on top of the foam and did not sink.
• the emulsion in the tub was cured by heating the tub I2 in a 60° C. incubator for 20.33 hours. 1.6 % of free water was poured off from the resulting foam.
• the probe After 110 minutes, the probe sat on top of the foam and did not sink.
• the emulsion in the tub was cured by heating the tub J2 in a 60° C. incubator for 19 hours. 2.21% of free water was poured off from the resulting foam.
• the probe After 61 minutes, the probe sat on top of the foam and did not sink.
• the emulsion in the tub was cured by heating the tub K2 in a 60° C. incubator for 18.25 hours. 6.65 % of free water was poured off from the resulting foam.
• This example demonstrates another preparation of a low density crosslinked polymeric material by advancing the monomer mixture according to the invention and comparison run N.
• a mixture-M was prepared in a similar manner to Example 5, except 100.23 g of monomer mixture (20.26 wt % styrene, 19.91 wt % divinyl benzene and 60.06 wt % of 2-ethyl hexyl acrylate) was mixed with 1.14 g of t-butyl peroxyisobutyrate (LupersolTM 80 from Atochem, North America) and 12.34g of Span® 20 emulsifying agent (sorbitan monolaurate from Fluka Chemical Corp. or Aldrich Chemical Co.).
• the probe After 114 minutes, the probe sat on top of the foam and did not sink.
• the emulsion in the tub was cured by heating the tub 02 in a 60° C. incubator for 22.75 hours. 6.02 % of free water was poured off from the resulting foam.
• the probe After 89 minutes, the probe sat on top of the foam and did not sink.
• the emulsion in the tub was cured by heating the tub P2 in a 60° C. incubator for 22.5 hours. 0% of free water was poured off from the resulting foam.
• the probe After 78 minutes, the probe sat on top of the foam and did not sink.
• the emulsion in the tub was cured by heating the tub Q2 in a 60° C. incubator for 22.25 hours. 4.36% of free water was poured off from the resulting foam.
• the foams produced according to the process of the invention (obtained from the advanced monomer mixture) have comparable or better foam properties compared with an unadvanced conventionally prepared material of N2.
• a 3:2 weight ratio of isoprene: divinyl benzene were mixed to produce a monomer mixture.
• 12 parts by weight for 100 parts by weight of the monomer mixture of a sorbitan monolaurate surfactant (SPAN® 20 emulsifying agent from Fluka Chemical Corp. or Aldrich Chemical Co.) was added.
• 1 part by weight for 100 parts by weight of the monomer mixture of LupersolTM 225 initiator (di(sec-butyl) peroxydicarbonate) from Atochem North America was added.
• the resulting mixture was advanced at the temperatures listed below. The high temperature advancement runs were performed in an autoclave blanketed with nitrogen under pressures up to 400 psig.
• aqueous phase containing 10% CaCl 2 was added slowly to the advanced monomer mixtures while stirring as in Example 5 to form a water-in-oil emulsion.
• 1 part by weight for 100 parts by weight of the monomer mixture of peroxide polymerization initiators or 0.14 part by weight for 100 parts by weight of the monomer mixture of potassium persulfate ("KPS") were added to the emulsion and mixed.
• KPS potassium persulfate
• the emulsions were poured into a 118 cm 3 (4 fluid oz.) jar and cured at 60° C.. Cure Time was determined by determining the time necessary for the emulsion to support a 2.1 kPa (0.3 psi) flat tipped probe at the surface of the emulsion and listed below in Table 7.
• the emulsion did not cure properly using benzoyl peroxide as the polymerization initiator without advancement.
• the emulsion cured to form a foam when benzoyl peroxide was used as an advancement initiator in the oil phase before formation of the emulsion.
• This example demonstrates another preparation of a low density crosslinked polymeric material by advancing the monomer mixture according to the invention.
• a 1:1:3 weight ratio of styrene: divinyl benzene:2-ethylhexyl acrylate were mixed to produce a monomer mixture.
• Synercial divinyl benzene containing 55% divinyl benzene from Aldrich Chemical Co. was used.
• 12 parts by weight for 100 parts by weight of the monomer mixture of a sorbitan monolaurate surfactant (SPAN® 20 emulsifying agent from Fluka Chemical Corp. or Aldrich Chemical Co.) was added.
• SPAN® 20 emulsifying agent from Fluka Chemical Corp. or Aldrich Chemical Co.
• LupersolTM 80 t-butyl peroxyisobutyrate from Atochem North America
• Example 5 To this advanced mixture an aqueous phase containing 10% CaCl 2 was added slowly to the advanced monomer mixture while stirring as in Example 5 to form a water-in-oil emulsion. No additional polymerization initiator was added. The emulsion was poured into a 1.5 liter (3 US pint) tub and cured at 60° C. for 16 hours. The properties of the foam are shown in Table 8 below.
• This example demonstrates another preparation of a low density crosslinked polymeric material by advancing the monomer mixture according to the invention.
• Example 10 B To these mixtures 1 part by weight for 100 parts by weight of the monomer mixture of LupersolTM 80 (t-butyl peroxyisobutyrate from Atochem North America) for Example 10 A and benzoyl peroxide (from Aldrich Chemical Co.) for Example 10 B were added. The resulting mixtures were advanced at 75° C. for 12 minutes.
• LupersolTM 80 t-butyl peroxyisobutyrate from Atochem North America
• benzoyl peroxide from Aldrich Chemical Co.
• Example 10A aqueous phase containing 10% CaCl 2 was added slowly to the advanced monomer mixtures while stirring as in Example 5 to form water-in-oil emulsions.
• aqueous phase containing 10% CaCl 2 was added slowly to the advanced monomer mixtures while stirring as in Example 5 to form water-in-oil emulsions.
• 1 part by weight for 100 parts by weight of the monomers of benzoyl peroxide for Example 10A and LupersolTM 80 for Example 10B were added and mixed.
• the emulsions were poured into a 1.5 liter (3 US pint) tub and cured at 60° C. for 16 hours.
• the properties of the foams are shown in Table 8 below.
• the foams produced by the advancement process of the invention have comparable to superior properties compared with the comparative example, Example 6, N2, particularly in foam absorption capacity such as Free Swell.

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• 1993
  • 1993-07-29 US US08/099,018 patent/US5290820A/en not_active Expired - Fee Related
  • 1993-11-29 US US08/159,072 patent/US5358974A/en not_active Expired - Fee Related
• 1994
  • 1994-01-24 JP JP7505786A patent/JPH09503531A/ja active Pending
  • 1994-01-24 WO PCT/US1994/000779 patent/WO1995004105A1/en not_active Ceased
  • 1994-01-24 EP EP94919062A patent/EP0712425B1/en not_active Expired - Lifetime
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